catalyst can likewise increase the reaction rate by enforcing this conform ##ation . similarly , β @ - @ substitution directed inward restrict ##s the s @ - @ trans conform ##ation so severely that e @ - @ z iso ##mer ##ization has been shown to occur in advance of cy ##cl ##ization on a wide range of substrates , yielding the trans cy ##cl ##open ##ten ##one regardless of initial configuration . in this way , the na ##zar ##ov cy ##cl ##ization is a rare example of a stereo ##sel ##ect ##ive per ##ic ##y ##cl ##ic reaction , whereas most electro ##cy ##cl ##izations are stereo ##sp ##ec ##ific . the example below uses tri ##eth ##yl ##sily ##l h ##yd ##ride to trap
catalyst can likewise increase the reaction rate by enforcing this conformation. similarly, β @ - @ substitution directed inward restricts the s @ - @ trans conformation so severely that e @ - @ z isomerization has been shown to occur in advance of cyclization on a wide range of substrates, yielding the trans cyclopentenone regardless of initial configuration. in this way, the nazarov cyclization is a rare example of a stereoselective pericyclic reaction, whereas most electrocyclizations are stereospecific. the example below uses triethylsilyl hydride to trap